1. Field of the Invention
The present invention relates to a projection apparatus for projecting an image by emitting light from a light source.
2. Description of the Related Art
Conventionally, a projection apparatus performs hold-type display. Hold-type display refers to, for example, continuously displaying the same image in a 16-ms frame duration at a 60-Hz frame frequency.
When displaying a moving image by a direct-view-type display apparatus, such as a television set, performing hold-type display will blur the moving image. A certain technique controls lighting of the backlight to solve this problem. For example, applying a technique for prolonging a black insertion duration enables improving the sharpness of the moving image. However, prolonging the black insertion duration means displaying an image having a 60-Hz frame frequency with a short light emission. In this case, a problem of flicker arises.
For example, Japanese Patent Application Laid-Open No. 2008-70838 discusses a display apparatus which performs a bright light emission for an original image and a dark light emission for an intermediate image. With such a display apparatus, although the above-described problem can be reduced to a certain extent, the image may be disturbed if an intermediate image generation error occurs.
Further, for example, Japanese Patent Application Laid-Open No. 2002-215111 discusses an image display apparatus which performs control to prolong the backlight lighting duration according to a required luminance.
Further, for example, Japanese Patent Application Laid-Open No. 2009-251069 discusses a display panel which performs control to prolong the backlight lighting duration in a period near the center according to a required luminance.
Japanese Patent Application Laid-Open No. 2011-28107 discusses a hold-type image display apparatus which emits light at two different luminance levels, i.e., performs bright and dark light emissions. Such a hold-type image display apparatus is able to reduce the above-described problem. However, if an image having a 60-Hz frame frequency is displayed with a short light emission, flicker occurs. If two short light emissions are performed within one frame to prevent flicker, a double image appears.
If an image is displayed at two different luminance levels as discussed in Japanese Patent Application Laid-Open No. 2011-28107, flicker is caused by the 60-Hz component in addition to the 120-Hz component. Therefore, the difference between the two luminance levels, if it gets larger, increases the amount of the 60-Hz component which generates strong flicker, making it harder for a viewer to watch an image. This means that the difference between the two luminance levels is limited. Further, the difference between the shapes of the original image and the intermediate image will cause a phenomenon of flicker around a displayed object.
However, prolonging the light-emission duration to brighten an image as discussed in Japanese Patent Application Laid-Open No. 2002-215111 causes strong tailing which is called a moving image blur.
Also when a moving image is displayed on a projection apparatus, a blur or flicker occurs similar to a direct-view-type display apparatus. However, it is difficult to apply the above-described techniques as they are to a projection apparatus since these techniques relate to a direct-view-type display apparatus.